Sep 152017
 

This morning the Cassini spacecraft entered the atmosphere of Saturn and ultimately became part of the planet it was sent to study.

Artist rendering of Cassini’s atmospheric entry.
Credit: NASA/JPL


The spacecraft entered orbit around Saturn on the 1st of July 2004 after a six year trip to the planet. It has been studying Saturn and its rings and moons since that time. One of the first things the spacecraft did was to deploy the Huygens probe toward Saturn’s largest moon, Titan. The probe became the first lander on a solar system moon other than our own.

Artist rendering of Huygens’ landing on Titan. Credit: NASA/JPL

Image from the surface of Titan. Credit: ESA/NASA/JPL/ University of Arizona

There are too many discoveries over the 13 years Cassini spent in the Saturnian system to list. Probably the most surprising was the discovery of geysers erupting from the southern pole of the ice covered moon Enceladus.

Geyser plumes from the southern pole of Enceladus. Credit: NASA/JPL


Subsequent study has revealed the material being ejected from the moon to be salty water carrying organic molecules. This implies the conditions necessary for life exists in the outer solar system in a place scientists never expected.

In addition to the scientific discoveries is the vast archive of images that Cassini took. The beauty of the planet and rings was worth the investment.

Saturn as seen by Cassini.
Credit: NASA/JPL


To the entire Cassini/Huygens team, thank you. Well done.

 Posted by at 10:24
Jul 032017
 

With my treeline obscuring Jupiter so quickly after sunset, I will reconfigure the PTO back to deep sky imaging tomorrow, the 2nd of July. So, this is the last JunoCam image until next year.
 

By mid March, Jupiter will become a morning target and rise above my eastern treeline by 0200. The PTO will resume supporting the JunoCam project then. How long the project lasts is all up to Jupiter’s radiation and NASA. The intense radiation is expected to eventually degrade each of the scientific instruments despite the spacecraft’s titanium shielding. If the instruments are no longer functional the Juno mission will end in July 2018. If some are still working it will be up to NASA to decide if additional funding is warranted to extend the mission.

 Posted by at 16:25
Jun 272017
 

The Earth’s orbit is taking us further and further from Jupiter. This means that the time I get to image Jupiter gets less and less as the Earth starts to round the Sun. Less time to image results in fewer candidate video streams.

Earlier in May it was dark before Jupiter cleared my eastern treeline and, once it was dark, I was able to get as many as 57 attempts. On the 22nd, I was only able to get 9 attempts before Jupiter hit the western treeline and after processing, only 1 of the 9 met the criteria for submission to NASA’s JunoCam site.

 Posted by at 17:05
Jun 192017
 

The sky last night was one of the darkest (and clearest) we have had in quite a few weeks. I was able to get a short JunoCam series before Jupiter hit my western tree line.
 

Ideally, if you want to image for an hour, the best time as far as the atmosphere is concerned, is the half-hour before the target gets to the zenith and the half-hour after it passes the zenith. But right now Jupiter gets only 55° high and is well past the meridian before the sky gets dark. That means the planet starts with less than optimal airmass and as the night progresses descends into ever increasing airmass.
 

Airmass is the length of the pathway through the atmosphere that the photons from the object you are looking at have to pass. The path length above the zenith is about 100 km and the path length along the horizon is about 1020 km. By definition, airmass is 1.0 for an object directly on the observer’s zenith. The lower in the sky, the higher the airmass gets. The longer atmospheric path means more distortion, absorption and refraction.

Close to the horizon, the object doesn’t look like it really does (distortion), isn’t as bright as it really is (absorption) and isn’t where it looks like it is (refraction).

 Posted by at 20:11
Jun 142017
 

Yesterday’s rain eased off and the clouds cleared around 2300. That gave me an opportunity to open up the dome and get a short series of Saturn images before the clouds closed back in. The atmosphere was fairly steady and the images showed it. Jupiter had already set below my western tree line so I was unable to get any additional images of Jupiter for NASA’s JunoCam project.
 

I was not the only one taking advantage of the clear sky. The other party posed for a selfie on the PTO’s all sky camera.

 Posted by at 20:06